Today's personal computer (PC) systems may include a processor which supports a system management mode. This system management mode (SMM) has various uses: handling low-level system events like memory or chipset errors; system safety functions, such as shutdown on high processor temperature; power management operations, such as turning on fans; and emulation of unimplemented motherboard hardware (e.g., a USB mouse appears to be a PS/2 mouse). A more recent use of SMM is to control access to various security features. It is desirable to allow trusted software components to control security features through SMM and prevent untrusted software components from doing so, while still allowing untrusted software components to use SMM for other purposes.